Despite a post-mortem and an investigation by the charity Cardiac Risk in the Young (CRY), Stuart's parents still have no definitive answer as to why their only son died on September 21, 2013.

Last night his father David urged parents to get their teenagers and young adults screened for any potentially fatal underlying heart conditions.

He and his wife Janet, their family, friends and supporters have raised more than £33,000 for CRY since Stuart's death to help fund the free screenings.

The fire officer from Islandmagee told the Belfast Telegraph: "Stuart was a big, strong, strapping fit young man and enjoyed his five-a-side football and swam. He was never sick to speak of.

"There was a post-mortem and then heart tissue was sent over to the CRY people in London, which was studied for several months. But they couldn't find anything physically wrong with him.

"Not knowing why Stuart died is one of the hardest things to come to terms with, but there are many others like him in the same boat.

"There is a high percentage of people who die from sudden death where it can't be said why it happened.

"But there are a lot of conditions which can be picked up by an electrocardiogram (ECG) test and can be treated."

Every week 12 apparently fit and health young people aged 35 and under die from undiagnosed cardiac conditions. There are no prior symptoms that gave concern for 80% of those who die.

CRY tests 17,000 young people aged 14-35 with free ECGs at a cost of £100 each to the charity.

Former Premier League footballer Fabrice Muamba's dramatic collapse and subsequent recovery while playing for Bolton Wanderers in 2012 highlighted the condition nationally.

While sport itself does not cause young sudden cardiac death, it will increase the risk by three-fold if the person has an undiagnosed underlying condition.

For David, Janet and their daughter Jennifer, life without Stuart over the past two years has been unbearable at times. They are eternally thankful for the aid that his team-mates and the Islandmagee first responders gave to Stuart when he collapsed, and for the support of family and friends who helped them in the weeks and months afterwards and who helped raise the money in through variety of ways.

David added: "Our house did not empty for weeks and weeks. The pain doesn't get any easier as the time goes on but your life adjusts to the loss. It's not a quick process, but hopefully we will get there.

"Stuart was a good big kid. He was just a joy to be around and was never in any trouble that I was ever aware of.

"No one ever said a bad word about him.

"From the day and hour he started work as an accountant technician, he hadn't a day off sick, and that was over six years.

"He had a girlfriend, Claire, for the past year.

"She doted on him, he doted on her, and they were a great wee couple.

"It was just brutal to lose Stuart like that. His team-mates were completely traumatised; in fact, everyone who knew him was.

"I would urge parents to go along to the CRY screening days as several of them are held here every year and it's completely free."

There are still places available from November 21-22 at Foyle College in Londonderry.

To book a free screening test, visit http://www.testmyheart.org/book-appointment/